When portions of granular or pulverized substances are obtained from a metering station which is mounted directly on the mixing vessel of a plastics processing machine, it has hitherto been common practice to detach the connection and to meter one or more portions into a measuring vessel in order to accurately define the weight of such portions and thus to define the metering ratio of various substances for a specific injection product of a plastics processing machine.
Such a procedure is time-consuming, since for this purpose the metering station must be detached from the mixing vessel above the plastics processing machine, at least temporarily, and must subsequently be mounted on the machine. The prior art already discloses automatic lifting devices for the purpose of effecting such temporary removal of the metering station from the mixing vessel, and one or more metering stations can be raised from the location of their use on the lid of the mixing vessel by means of such lifting devices, for example pneumatically, by the distance which is necessary in order to remove the samples. Such lifting work to a height of 20 to 30 cm above the lid of the mixing vessel calls for complex additional apparatus and cannot be embodied in every case, since the structural height above the metering stations at the location of use of the injection moulding machine is frequently limited.
In order to obtain precise determination of the partial quantities contained in the individual chamber volumes of the metering disc of disc metering devices, for example according to German Patent Specification No. 19 47 405, or in gear metering devices, for example according to German Patent Specification No. 22 14 982, it has hitherto been the practice to collect a specific number of partial quantities, for example ten, in a separate measuring vessel in order to define the weight of such partial quantities and to adjust the metering device accordingly.
A method of this kind becomes even more time consuming and therefore more expensive if a plurality of metering stations are flange mounted on a mixing vessel, for example one metering station for the principal component of the plastics material, a second station for the regenerate, and a third for the pigment. In this case it is necessary for the procedure and removal and weight determination to be performed three times.
It would therefore be desirable to arrange the initially mentioned apparatus so that the described method for removing partial quantities of substance to be metered can be simplified and can be performed more rapidly without the need for moving, at least temporarily, one or more of the metering devices from the mixing hopper of the plastics processing machine.